Guaiac-based Fecal Occult Blood Test (gFOBT)

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What Is the Guaiac-based Fecal Occult Blood Test?

Fecal occult blood tests are often abbreviated as FOBT, and you might come across this abbreviation when looking over a patient’s orders. Occult essentially means hidden or hidden from the naked eye. Therefore, the guaiac-based fecal occult blood test aims at detecting blood loss in the GI tract through blood testing.

Guaiac fecal occult blood test is often seen in the emergency setting. There are high sensitivity guaiac tests or Hemoccult stool tests as the Hemoccult Sensa and older guaiac test such as the Hemoccult II. These tests rely on the oxidation of guaiac paper by hydrogen peroxide, catalyzed by the peroxidase activity of hemoglobin – gFOBT is capable of detecting bleeding from any region of the GI tract. Though some institutes are moving away from the gFOBTs, several prefer gFOBT tests. 

Guaiac Fecal Occult Blood Test for Early Detection of Colorectal Cancer

Every year, more than 140,000,000 are diagnosed with colon cancer and 60,000,000 succumb to it. Men, women, and children from all ethnic groups and backgrounds are affected by colorectal cancer. However, the disease is most likely to occur in people over 50. The good news is that colon cancer can be prevented and even cured with early testing.

Guaiac-based fecal occult blood test is the most useful method to detect colon cancer. Before cancer develops, tissue growth usually starts as a non-cancerous polyp on the inner lining of the colon. A stool guaiac test detects the presence of occult blood in a stool sample that can be caused by cancerous tumors or polyps in the intestines.

How to Prepare for The Test?

The guaiac test kit includes a set of three cards each. Each card has two boxes, used to collect the stool sample over three days. There are applicator sticks, used to collect the stool – also present is a special envelope which allows you to mail back the stool sample.

Do not eat any citrus fruits like lemon, grapefruit, and orange, juice or vitamin C supplements, three days before the test. Besides, red meat such as beef, lamb, or liver should be avoided 3 days before and during the test. Medications for diarrhoea, heartburn, stomach pain (period cramps) should be stopped 3 days before the test as well as during the test. You can resume all these once your gFOBT test is done.

Collecting the Sample

Each time before collecting your stool sample, you should fill out all the information on the front of each card. There are many methods of collecting your stool sample. But you must collect it properly to avoid contamination. To collect your stool sample, you can put toilet paper in a clean container. Another method would be to turn off your water supply to the toilet. The water supply valve is usually located behind and below your toilet’s flush tank. Once you close the water supply valve, flush your toilet once and there should be no more water left in the bowl. 

Now you can place some toilet paper inside the toilet. After you have your bowel movement, use the applicator stick to collect some of your stool. After collecting the stool, smear a thin stool sample in the box labelled “A”. Then use the same stick to get a different stool sample and smear it accordingly in the box labelled “B.” Let the samples dry and then close the card. After collecting the stool sample, be sure to wash your hands using soap and water. Remember to turn on your water supply valve behind your toilet and then flush your toilet thrice. 

Continue to use the same method to collect the second and third stool sample until all the cards have samples. Follow the above-mentioned procedure whenever you collect a stool sample. Remember that during this period, you must maintain the food and diet restrictions until all the samples have been collected. Once all the cards have the samples, place them in your envelope. Then send them to the laboratory or return them to your doctor’s clinic as soon as possible.

What Do the Results Indicate?

Positive tests or positive “stool” warrant further evaluation for peptic ulcers, polyps, or malignancy.  In simpler words, if your guaiac-based fecal occult blood test returns positive, it indicates that there is abnormal bleeding (occult blood) occurring somewhere in your digestive tract (DI).  However, bleeding around the DI could be caused by several conditions and doesn’t always mean cancer. Therefore, the positive results are often followed by endoscopy or a colonoscopy to determine the source which can help detect colorectal cancer.

If the FOBT is positive, please see a primary care provider to arrange for a colonoscopy. Always ensure that your primary care provider or medical practitioner explains your results before undergoing colonoscopy. 

 

FAQs:

How Accurate Is the Guaiac fecal occult blood test (gFOBT)?

Although no screening test is 100% accurate, the gFOBT test is slowly gaining popularity and is now available widely and well-trialled screening test for early detection of colorectal cancer. On average, it is advised to do a gFOBT test periodically to reduce the risks associated with colorectal (bowel) cancer

Are there any disadvantages to the test?

These tests rely on the oxidation of guaiac paper by hydrogen peroxide catalysed by the peroxidase activity of haemoglobin. The disadvantage of this reaction is that it will occur with any peroxidase found in your faeces such as the peroxidase found in digestive plants and red meat. Also, the reaction is affected by certain medications or supplements. In simple words, certain foods can medicines can result in a false positive

Does the Test Impact your Decision to Undergo a Colonoscopy?

The result of an FOBT has an insignificant impact on whether the asymptomatic patient undergoes an exploratory endoscopy or colonoscopy. If there is clinical evidence of blood loss such as unexplained anaemia, a patient is likely to get a scope of the gastrointestinal tract regardless of the FOBT result. 

Why Collect 3 Samples?

The guaiac fecal test is used for detecting blood hidden to the naked eye. This occult blood often originates from large polyps or from colon cancers that tend to reside on the colon walls. As the colon gland pushes your stool out, the stool tends to circulate through the colon walls. However, during this circulation, the stool picks up the cancer blood. Although, the colon changes shape during its functioning. Therefore, collecting three samples, each with a bit of stool from two different spots largely increases the chances of finding the hidden blood originating from the colon cancer or large polyps

Who Should Undergo The gFOBT?

If you are between the ages of 50-70 and do not have a family history of colorectal cancer, you should get screened for the stool test or a guaiac test. If you have a history of colorectal cancer, please let your primary care provider know as you will need a different test called a colonoscopy instead of the FBOT or gFOBT.